N-type bismuth vanadate (BiVO4) has recently emerged as a promising photoanode for use in water-splitting photoelectrochemical cells because it absorbs a substantial portion of the visible spectrum and has a favorable conduction band (CB) edge position very near the thermodynamic H2 evolution potential. However, the solar-to-hydrogen conversion (STH) efficiency achieved with BiVO4 to date has been far below what is expected because the material suffers from poor electron-hole separation yield (φsep). Previous efforts to improve the φsep of BiVO4 mainly focused on doping studies, which were intended to improve its poor electron transport properties.
A porous BiVO4 material has been made by applying V2O5 dissolved in aqueous NH4OH solution onto a BiOI substrate, followed by conversion to BiVO4. However, because the hydrophilic V2O5-containing solution could not wet the hydrophobic surface of BiOI, the resulting BiVO4 electrodes were composed of large submicron size particles, limiting the surface area and photoelectrochemical performance of the material. (See McDonald et al., Energy Environ. Sci. 5, 8553-8557 (2012).)